Marihuana and the eye

.he first report of a decrease in intraocular pressure following smoking of marihuana was received with a fair amount of skepticism, mirth, and bad publicity in the press, such as articles informing the public of a new "cure" for glaucoma. Now that the smoke has cleared, it is time to evaluate the effects of marihuana on the eye and make an objective assessment of the potential therapeutic value of this drug (rather, a group of drugs) in ophthalmology, while putting aside the moral and ethical discussion of the use of marihuana in society as a drug of abuse. Many questions are immediately forthcoming. Does the drug really act to consistently reduce intraocular pressure? If so, how does it work? What are the side effects? Can one use a topical drop? Is there a compound which is active as regards intraocular pressure without producing undesired systemic and central effects? Some of these questions can be answered at this time while others await more detailed examination. It is now well documented that marihuana, or its primary active ingredient delta-9-tetrahydrocannabinol (A' THC), when given to rabbit or man by several routes, reduces intraocular pressure. The group at UCLA, continuing their initial efforts, find that chronic smoking of marihuana by inpatients (average of 15 "joints" per day for 94 clays) always causes an intraocular pressure fall which lasts for four to five hours even after one "joint."The intraocular pressure decrease appears to be unrelated to the total number of cigarettes smoked, suggesting that the plasma dose of THC reached after one cigarette is sufficient to evoke the maximal response. No immediate or cumulative effects were observed on any measure of ocular status, including visual fields, visual acuity, tonography, slit lamp biomicroscopy, electroretinogram (ERG), and the appearance of the lundus. Only ocular pulse pressure and tear secretion decreased after THC, both by statistically significant amounts, together with a slight pupillary constriction. In patients with ocular hypertension or glaucoma, seven of 11 patients showed an intraocular pressure fall of 30 per cent. Another study, however, also utilizing confined patients,' revealed that a tolerance developed to the oral administration of A-THC; the dose level, however, was much higher than that used in the study where the marihuana was smoked. The intraocular pressure showed an initial fall after oral use and returned to baseline as tolerance developed. Further smoking of marihuana in this patient group failed to cause a fall in intraocular pressure. Prob-